NASA announces discovery of Earth-like planet with earth similarity index 0.98 • Hacker News Board

Re: NASA announces discovery of Earth-like planet with earth similarity index 0.98

#101

Post by comrade1 » Thu, Jul 23, 2015, 2:46 PM UTC

allcentury wrote: post #3

dr_zoidberg wrote: post #2

As of now, the content linked says nothing more than the PR announcement from yesterday -- so either the title is misleading, or the OP comes from the future. (I'm aware he might have other sources for the title, but it's still misleading)

I think the announcement is live at noon today (EST).

Only on HN would a discussion about the discovery of an earth-like planet devolve into a discussion on the proper use of time zones...

Re: NASA announces discovery of Earth-like planet with earth similarity index 0.98

#102

Post by weland » Thu, Jul 23, 2015, 2:46 PM UTC

Osmium wrote: post #64

haarts wrote: post #26

It's interesting to note that the highest ESI so far has been Kepler-62e with a score of 0.83 ( https://en.wikipedia.org/wiki/Earth_Similarity_Index ). So a score of 0.98 would seem significant.

Question: why is 'escape velocity' part of the Earth Similarity Index when, presumably, it's just a function of radius and density (which are also in the index)? I feel like I'm missing something.

It's a reasonable measure of surface gravity, which, along with an idea about the distance from the star it's orbiting, gives us a good idea about what kind of atmosphere we can expect (i.e. the lighter and the hotter a gas is, the easier it can escape a planet with a particular escape velocity), at least a basic idea about what kind of surface features we might expect and so on.

It's also a parameter that is quick to compute starting from radius and mass, which are often the first things you know about an exoplanet due to the way they're found.

Re: NASA announces discovery of Earth-like planet with earth similarity index 0.98

#103

Post by almost_started » Thu, Jul 23, 2015, 2:48 PM UTC

It HAD an ESI of 0.98 1075 years ago. By now, the inhabitants have burned through all their fossil fuels and then annihilated each other with nuclear weapons leaving the planet in both a long-term nuclear winter and with a runaway greenhouse effect. Its ESI must be at least 1.0 by now.

Re: NASA announces discovery of Earth-like planet with earth similarity index 0.98

#104

Post by sixothree » Thu, Jul 23, 2015, 2:52 PM UTC

V-2 wrote: post #98

This similarity index only measures radius, density, escape velocity and surface temperature, so it doesn't mean nearly as much as one would think upon reading the headline

Does surface temperature imply an awful lot in this situation? How accurate are we able to measure?

Re: NASA announces discovery of Earth-like planet with earth similarity index 0.98

#105

Post by joshstrange » Thu, Jul 23, 2015, 2:55 PM UTC

danielweber wrote: post #93

danielweber wrote: post #83

Earlier quoted context omitted.

People think they are being more precise by saying "EST," but, quick, are we in daylight savings time now, or out of it? It turns out we are, and I don't meant to suggest that GP didn't know this. But what if we weren't in daylight savings time, and GP said "EST"? Would we have to change an hour? I highly recommend just saying "Eastern Time."

Crap, I was wrong. "S" doesn't stand for "Savings," it stands for "Standard." We really are in EDT. All the more reason to never specify it! :)

Welcome the world of pain that is timezones and DST... As someone who has had to write an extensive amount of deal with these two concepts they are the worst things ever. We should just abolish timezones, DST, and move to the International Fixed Calendar. Time sucks. I'm even in favor of moving to a seconds-based time unit like kiloseconds, miliseconds, etc instead of minutes/hours/days/weeks/months/years/etc. "Metric Time" if you will...

Re: NASA announces discovery of Earth-like planet with earth similarity index 0.98

#106

Post by fredley » Thu, Jul 23, 2015, 2:55 PM UTC

xamdam wrote: post #100

ELI5: until we flew next to Pluto this month all we had is blurry 16-pixel images. How can we get such precise data on something millions of times further?

The similarity index measures things that can be worked out without needing a precise image of the planet. These are things like radius, density and surface temperature, which can be measured by examining its orbit and how much light from the star is blocked as it passes.

Re: NASA announces discovery of Earth-like planet with earth similarity index 0.98

#107

Post by [deleted] » Thu, Jul 23, 2015, 2:55 PM UTC

almost_started wrote: post #103

It HAD an ESI of 0.98 1075 years ago. By now, the inhabitants have burned through all their fossil fuels and then annihilated each other with nuclear weapons leaving the planet in both a long-term nuclear winter and with a runaway greenhouse effect. Its ESI must be at least 1.0 by now.

[deleted]

Re: NASA announces discovery of Earth-like planet with earth similarity index 0.98

#108

Post by mc808 » Thu, Jul 23, 2015, 2:56 PM UTC

xamdam wrote: post #100

ELI5: until we flew next to Pluto this month all we had is blurry 16-pixel images. How can we get such precise data on something millions of times further?

1. Only compare radius, density, escape velocity, and surface temperature.

2. Ignore the confidence intervals around those values.

Re: NASA announces discovery of Earth-like planet with earth similarity index 0.98

#109

Post by objclxt » Thu, Jul 23, 2015, 2:56 PM UTC

xamdam wrote: post #100

ELI5: until we flew next to Pluto this month all we had is blurry 16-pixel images. How can we get such precise data on something millions of times further?

Nearly all of the ways we detect exoplanets involve indirect observation. Most of them are based on observing the star(s) in the system of the planet. The two main ways we detect exoplanets are:

* Radial Velocity - just as the gravity of a star effects a planet's orbit, the gravity of a planet also has an impact on the star's. It's just this impact is extremely small. By measuring variations in a star's movement due to the planet's gravity we can both detect the planet and estimate its mass.

* Photometry - when a planet moves in front of a star it reduces both the brightness and spectrum of the light we perceive. By carefully measuring this we can determine not only the size of the planet, but also it's chemical make-up - light from the star travels through the atmosphere of the planet, changing its spectrum in response to the elements present.

There are several other ways we can detect and examine planets, but nearly all of them are based not on observing the planet itself but its impact on much larger, detectable things that surround it. There's a comprehensive list here - https://en.wikipedia.org/wiki/Methods_of_detecting_exoplanet...

Re: NASA announces discovery of Earth-like planet with earth similarity index 0.98

#110

Post by slater » Thu, Jul 23, 2015, 2:57 PM UTC

xamdam wrote: post #100

ELI5: until we flew next to Pluto this month all we had is blurry 16-pixel images. How can we get such precise data on something millions of times further?

IANAAP, but I saw a similar question about how the Hubble space telescope could only get blurry pictures of Pluto. The answer was that it was akin to using a microscope as a telescope (or vice-versa), if that makes sense?